Sian Ka'an Biosphere Reserve

Jaguars, ocelots, and tapirs, as well as hundreds of species of birds and fish, roam these 1.3 million acres of coastal jungle, home to nearly every Yucatán ecosystem and studded with unexcavated ruins. The only way to explore the World Heritage site is on tours that follow 1,200-year-old trade routes on foot and by boat with trained volunteers, marine biologists, and other scientists, some of whom have lived in the reserve for ages; the guides discuss Mayan history and present-day ecological challenges.